1. Field of the Invention
The present invention relates generally to an optical resonator having a two resonator mirrors for use with a laser.
2. Description of the Related Art
An optical resonator having a pair of opposed resonator mirrors for a gas laser is disclosed in German Patent No. 31 51 228. The resonator mirrors are arranged at the end faces of a glass-ceramic mirror carrier, the end faces being ground and optically polished. In lasers of the type disclosed in the German Patent No. 31 51 228, optimum feedback is accomplished by providing an absolute distance L between the two resonator mirrors, the distance L being defined as n.times.x.lambda./2, where n is a whole number &gt;&gt;1. The distance L must be extremely precisely observed in a range of 1/10 micrometers through 1/100 micrometers. These high precision demands made of the resonator link L, however, are extremely difficult to meet when grinding and optically polishing the end faces of a mirror carrier.
For frequency tuning of gas lasers, it known from the publication Laser Handbook, Volume 3, 1979, North-Holland Publishing Company, pp. 71-78 to use a reflecting, optical grating instead of a second resonator mirror. The wavelength of the laser emission being tuneable on the basis of the angular position of the grating relative to the optical axis of the resonator. Optical gratings, however, are expensive and involved and result in optical losses.
From the publication Kleen/Mueller, Laser, Springer-Verlag (1969), pp. 310-313, it is known to set a resonator length through the use of piezo-electric elements to frequency tuning of a gas laser. The resonator mirrors are mounted on piezo ceramic mounts to enable the resonator length to be precisely determined. Such piezo-electric length adjustments, however, require involved control circuitry. Moreover, the piezo-electric adjustments cause amplitude modulation and frequency modulation, which is undesirable in highly stable systems.